An exhaust gas turbocharger on an internal combustion engine uses the energy of the exhaust gases output by the internal combustion engine to drive a turbine which is coupled to a compressor that compresses a fresh gas for the internal combustion engine. To boost the power of a turbocharger of this kind, a valve in the form of an exhaust gas flap (“wastegate”, “bypass valve”) can be used, said valve directing a portion of the exhaust gas flow past the turbine into an exhaust gas system. The exhaust gas flap is usually integrated as a spherical slide valve or similar structure into the turbine housing. The exhaust gas flap is moved by an actuator having a transmission mechanism. The actuator can be an electric positioning motor or a pneumatic device with electropneumatic pressure control, for example. The actuator can have a position transmitter for determining the position of the actuator.
The position of the exhaust gas flap is used directly to control the power of the turbocharger and hence indirectly also to adjust the required boost pressure of the fresh gas of the internal combustion engine and hence of a required engine mode. For this reason, incorrect positioning of the exhaust gas flap can cause engine behavior which deviates from the required engine behavior. The deviation can be relevant to safety if the internal combustion engine outputs more than a required power, for example. If, for example, the internal combustion engine is driving a motor vehicle, unwanted acceleration of the motor vehicle can occur as a result.
The actual position of the exhaust gas flap is normally monitored, therefore. In addition or as an alternative to determination of the position of the exhaust gas flap, the operation of the exhaust gas turbocharger can be subject to plausibility checking through observation of a boost pressure. If the boost pressure does not correlate with a desired position of the exhaust gas flap, however, it is still not possible from this to deduce a specific fault since, for example, a leak downstream of the compressor or contamination of an air filter can have a similar effect to an exhaust gas flap which can no longer be fully closed.